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Subject[PATCH v4 08/14] arm64: exec: Adjust affinity for compat tasks with mismatched 32-bit EL0
Date
When exec'ing a 32-bit task on a system with mismatched support for
32-bit EL0, try to ensure that it starts life on a CPU that can actually
run it.

Signed-off-by: Will Deacon <will@kernel.org>
---
arch/arm64/kernel/process.c | 42 ++++++++++++++++++++++++++++++++++++-
1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 1540ab0fbf23..72116b0c7c73 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -31,6 +31,7 @@
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/cpu.h>
+#include <linux/cpuset.h>
#include <linux/elfcore.h>
#include <linux/pm.h>
#include <linux/tick.h>
@@ -625,6 +626,45 @@ unsigned long arch_align_stack(unsigned long sp)
return sp & ~0xf;
}

+static void adjust_compat_task_affinity(struct task_struct *p)
+{
+ cpumask_var_t cpuset_mask;
+ const struct cpumask *possible_mask = system_32bit_el0_cpumask();
+ const struct cpumask *newmask = possible_mask;
+
+ /*
+ * Restrict the CPU affinity mask for a 32-bit task so that it contains
+ * only the 32-bit-capable subset of its original CPU mask. If this is
+ * empty, then try again with the cpuset allowed mask. If that fails,
+ * forcefully override it with the set of all 32-bit-capable CPUs that
+ * we know about.
+ *
+ * From the perspective of the task, this looks similar to what would
+ * happen if the 64-bit-only CPUs were hot-unplugged at the point of
+ * execve().
+ */
+ if (!restrict_cpus_allowed_ptr(p, possible_mask))
+ goto out;
+
+ if (alloc_cpumask_var(&cpuset_mask, GFP_KERNEL)) {
+ cpuset_cpus_allowed(p, cpuset_mask);
+ if (cpumask_and(cpuset_mask, cpuset_mask, possible_mask)) {
+ newmask = cpuset_mask;
+ goto out_set_mask;
+ }
+ }
+
+ if (printk_ratelimit()) {
+ printk_deferred("Overriding affinity for 32-bit process %d (%s) to CPUs %*pbl\n",
+ task_pid_nr(p), p->comm, cpumask_pr_args(newmask));
+ }
+out_set_mask:
+ set_cpus_allowed_ptr(p, newmask);
+ free_cpumask_var(cpuset_mask);
+out:
+ set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+}
+
/*
* Called from setup_new_exec() after (COMPAT_)SET_PERSONALITY.
*/
@@ -635,7 +675,7 @@ void arch_setup_new_exec(void)
if (is_compat_task()) {
mmflags = MMCF_AARCH32;
if (static_branch_unlikely(&arm64_mismatched_32bit_el0))
- set_tsk_thread_flag(current, TIF_NOTIFY_RESUME);
+ adjust_compat_task_affinity(current);
}

current->mm->context.flags = mmflags;
--
2.29.2.454.gaff20da3a2-goog
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